Eighteen-year-old Fujita was reportedly distraught after Astley ended their three-year relationship last April, sending her a letter pleading, "I truly think there's part of you that still loves me, you just have to let me find it."

Astley, also 18, whose body was found July 4 in a swamp near the couple's hometown of Wayland, Mass., responded with a series of text messages trying to set up a time to talk.

"In an act of friendship, Lauren Astley reached out to the defendant," prosecutor Lisa McGovern said Tuesday at the Middlesex Superior Court arraignment where the new details emerged. "He reciprocated this act of friendship by killing her."

Fujita pleaded not guilty Tuesday to the charge of first-degree murder and was ordered held without bail until Sept. 22, when his defense attorney plans to push for his release on bail.

Fujita, in custody since his arrest in July, also pleaded not guilty to two counts of assault and battery with a dangerous weapon and a single count of assault and battery.

Astley's body was found in the swamp by a passing bicyclist. Her throat had been slashed and a jagged-edge, leaving a gaping wound across her neck.

Romance Ends In Murder

Prosecutors, who say Fujita brutally beat then strangled his former sweetheart with a Bungee cord, have presented the murder as a case of alleged teen dating violence.

"Lauren broke off the relationship. … It's a classic fatal paradigm that we see around teen dating relationships," Middlesex District Attorney Gerard T. Leone told reporters at a news conference last month.

Astley's friends told police he had an "on again, off again" relationship with Astley after she broke up with him in April. They also said Fujita had been less social and also seemed angrier for the past several weeks.

He had reportedly called Astley several times on her cell phone at the Shop344 store in the Natick Collection Mall where she worked. Cell phone records show three calls between Fujita and Astley the night before her body was found.

Fujita's mother also reportedly secretly visited Astley, an aspiring fashion design designer, at the Shop344 store, telling her that she was worried about her son's well-being after their breakup.

The two families reportedly shared a close bond. Astley even interviewed Tomo Fujita, Nathaniel's father, for a school project posted on YouTube in June 2010.

Astley's father, Malcolm Astley, expressed empathy for Fujita's family at a court hearing last month but at Tuesday's hearing, he could be seen in the courtroom weeping as details about his daughter's gruesome death were revealed.

"Our hearts are with the many who continue to feel the shock and pain of the tragedy and try to understand it as best we can," he said Tuesday outside the courtroom.

Tuesday's arraignment also painted a more detailed portrait Fujita's actions after the crime.

The new court papers say Fujita drove the night of July 3 from the Water Row swamp, where Astley's body was found, to his parents' nearby home, then called and asked them to come home so the family could watch a movie together.

Fujita was spotted driving shirtless, with his car windows down and music blaring.

He also called a cousin later that night, explaining to prosecutors, "I just wanted to get my mind off of it."

Lauren Astley Goes Missing

When Astley didn't return home from her job at a clothing boutique the night of July 3, it was her father who filed a missing person's report with the Wayland Police Department.

Police questioned Fujita shortly afterward. He said Astley had visited their home around 7:45 p.m. then left after they spoke briefly while she remained in her car.

Police later searched Fujita's home, where he lives with his parents. They found blood in the garage and on an exterior door handle, and traces of blood on the kitchen floor, kitchen sink and bathroom sink.

They found a pair of blood-spattered sneakers in an attic crawlspace above Fujita's room.

Police also discovered a plastic garbage bag filled with bloody water-logged clothing, including a sweatshirt with pockets containing dirt similar to that of the marshland where Astley's body had been found.

Fujita had been planning to attend Trinity College in Connecticut this fall.

Astley, who also recently graduated from Wayland High School, had been accepted to Elon University in North Carolina. Her father told the Boston Globe Astley was their only child, and said she was a former captain of the high school tennis team who sang in her school's a capella group and wanted to work in the fashion industry.

Fujita doesn't have a previous criminal record, and there is no indication that Fujita had abused Astley while they were dating, District Attorney spokeswoman Jessica Venezia Pastore said.